TEMPERATURE SENSES IN FROG's SKIN 85 



Rosenthal, '75) maintained that cold caused a depression in 

 reflex excitability, except in the case of ice packs, which in- 

 creased it (Richardson, '67; Weir-Mitchell, '67; Wundt, '67), 

 and another group were of the opinion that heat properly ap- 

 pUed also caused excess excitability (Cayrade, '64; Goltz, '69; 

 Tarchanow, '71, '72; Freusberg, '75). 



When cold or heat are applied very gradually to a frog the reactions 

 decrease in extent and vigor. There has been a good deal of dis- 

 agreement in the literature, regarding reactions to gradually 

 applied stimuli. The question was opened by Goltz ('69), who 

 immersed normal and reflex frogs in water of gradually increasing 

 temperatures. When slowly stimulated up to 30°C., the normal 

 frog became violent, but the reflex frog remained inert. Goltz's 

 main purpose had been to show the difference between the two 

 conditions in the animal, and he immediately declared the lassi- 

 tude of the reflex frog due to its brainless state. By the same 

 method, Tarchanow ('71, '72) secured similar results on normal 

 frogs. The next year Heinzmann ('72) continued similar ex- 

 periments from the point of view that the sensory nerves might 

 be affected by a stimulus increasing in intensity so slowly that 

 destruction of the nerve would result before a reaction could 

 occur. Normal and reflex frogs were heated with the expected 

 results to both of them, and these were explained as due to the 

 very gradual succession of the stimuli. In 1875 Fratscher re- 

 peated these expermients with identical results. The quiet 

 normal frogs of Heinzmann and Fratscher were thus pitted 

 against the violent normal frogs of Goltz and Tarchanow, but 

 the main conclusion seems to have been that no reaction would 

 result if stunulation were applied with sufficient gradualness. 



Foster ('73) had previously questioned Goltz'^ -^^atement that 

 brainless frogs would give no reaction to stimuli to which normal 

 frogs reacted so vigorousl}^ He immersed reflex frogs 'locally 

 and totally' and obtained xevy difl'erent results in the two cases. 

 When large areas of the body were immersed there was no re- 

 sponse, but when only the toes were dipped, no matter how 

 gradually the heat was increased, they were alwaj^s withdrawn 

 at about 35°C. This peculiar result was explained by Foster 



